This invention relates to the field of duplication wherein heat fixing systems for fixing images on powdered thermoplastic marking media to receptor surfaces, e.g. in high speed automatic copiers or reproducers, are utilized. More particularly it relates to an improved fusing blanket construction for use in such fixing systems.
The use of thermoplastic resin material in particulate form for the purpose of forming images on paper in copying machines or the like has generated various devices for adhering the particulate material to the desired receptor surfaces, especially in the form of sheets. It is necessary that the particulate resin material, hereinafter referred to as ink or toner powder, be fused or softened to a tacky state such that it can adhere to the receptor surface, and upon cooling will be bonded to the receptor surface to form images thereon. It is important in fixing the ink to the receptor surface that the ink is not disturbed as far as location on the receptor surface and that the ink is not offset so as to distort the image character.
Fusing devices which have been utilized for this image fixing generally include a pair of nip rolls, one being a heated fusing roller having a peripheral surface which has a low affinity for the fused or softened ink, and the other being a pressure or backup roll. The receptor element, generally a sheet of paper, bearing the particulate ink advances between the nip area of the rollers whereby the ink is to be fused and bonded to the receptor surface. The peripheral surface of the fusing roller must have a sufficiently low affinity for the softened ink such that the tacky ink particles preferentially adhere to the receptor surface rather than the fuser roll surface. If these particles do stick to the fuser roll surface, a splitting of the image occurs, such that a partial or ghost image results on the next advancing sheet, producing what is commonly termed in the duplicating art an offset image.
One approach to providing a surface for the fusing roller which has a low affinity for the softened ink is by using nip rolls which may be coated with a tetrafluoroethylene resin such as Teflon and a system for dispensing a silicone oil (a dimethyl siloxane polymer) onto the heated fusing roll, as taught by U.S. Pat. Nos. 3,291,466; 3,331,592; 3,449,548; and 3,452,181.
Another method, designed to eliminate problems encountered with liquid dispensing systems, is to provide a silicone elastomer surface for the heated fusing roll, as is taught in U.S. Pat. No. 3,669,707. However, the silicone elastomer surface is subject to abrasion and chemical interaction with the ink particles, which does cause a long-term loss in effectiveness.
A recent improved fusing device, as disclosed in copending and commonly assigned U.S. patent application, Ser. No. 103,725, filed by Gorka et al on Jan. 4, 1971, now U.S. Pat. No. 3,716,221 granted Feb. 13, 1973, utilizes a fusing blanket comprised of a thin, flexible heat-conductive substrate, such as stainless steel, having bonded thereto a silicone elastomer, which can be removably mounted on a heated fusing roll. During operation an offset preventing fluid, e.g. silicone oil, is applied to the silicone elastomer surface of the fuser blanket. The silicone elastomer surface is, however, somewhat penetrable by the offset preventing liquid. It has been found that this penetration can tend to cause a failure of the bond between the heat-conductive substrate and the silicone elastomer overlayer over a period of time, eventually resulting in delamination of the blanket.
This invention provides a fusing blanket which retains the beneficial silicone elastomer surface for offset prevention and allows utilization of a dispensed fluid such as silicone oil without any attendant delamination problem. This is accomplished by providing a fuser blanket in the form of a composite construction of a heat-conductive substrate having bonded thereto, in ascending order, a fluorinated elastomeric polymer and a silicone elastomer. While the silicone elastomer is penetrable by offset preventing fluids such as silicone oil, the fluorinated elastomer is substantially impenetrable. Also, the bond between the silicone and fluorinated elastomers is not affected by penetration of the fluid. Thus delamination of the fuser blanket is effectively prevented, resulting in a longer-lived fuser blanket.